and fiducial marks have to be located and all auto-
matic operations have to be followed by verification
and editing. Reducing of the cost of hardware and on
the other hand high cost of labour with the increased
demand for spatial data for GIS will cause desire for
other automatic operations.
At this moment most photogrammetric operators are
not skilled in the management of large data volumes
(GBytes of data in computer files) and the complex
manipulation of the DPW software. The operator
can be less skilled in photogrammetry but should be
more skilled in computer operations in the future. It
is likely that a new type of photogrammetric special-
ist is to emerge. They will be experts in software
and file manipulation who has developed expertise in
the photogrammetric operations. The use of standard
PC environment can significantly help in technology
utilization, make photogrammetry more wide-spread
as well as decrease expenses on labour training and
wages.
3 PhoTopoL
In this section we would like to introduce a live ex-
ample of cost-effective solution for digital photogram-
metry based on our product PhoTopoL. PhoTopoL is
a powerful low-cost software application developed by
Help Service - Mapping Ltd. (Prague, Czech Repub-
lic) for production of precise maps from aerial photog-
raphy. The system is supplied in three versions with
gradual levels of functionality. The most advanced
version of the system provides all main functionality
of DPW mentioned above.
PhoTopoL performs orthorectification to remove geo-
metric distortions and the effects of terrain relief dis-
placement in aerial photos. PhoTopoL also produces
Digital Elevation Models by correlation of stereo pair.
Its stereo plotting capabilities provide very good tool
for preparation and updating digital maps and DEMs.
More over full-featured GIS system (TopoL) is in-
cluded in PhoTopoL and all data are captured directly
for the use in TopoL GIS. PhoTopoL is running on a
standard personal computer in MS Windows environ-
ment.
3.1 Image orientation
PhoTopoL supports image stereo pair parameter set-
tings, such as internal and external orientation ele-
ments, and image orientation calculations. Absolute
orientation of a photo or a stereo pair can be calcu-
lated on the basis of following methods:
e standard relative orientation and spatial trans-
formation of a DEM into ground coordinates
e Bundle Adjustment method
302
To calculate an absolute orientation of one image or
a stereo pair, it is necessary to provide following pa-
rameters:
e camera parameters (calibration protocol), focus
length, coordinates of fiducial marks
e flight altitude (approximate, not quite impor-
tant), which is usually printed on the photo-
graph
e four fully specified (X, Y, Z coordinates) control
points at least
3.2 Orthorectification
PhoTopoL provides orthorectification functionality.
Orthorectification removes the effects of relief dis-
placement and imaging geometry from aerial photos.
Rectification can be done in our system pixel by pixel
or by triangles where users are able define the size of
triangles. In that case the system works faster but
one has to take into account the relief of scene and
the influence of generalization when it is substituted
by network of triangles. Grey values or colours can
be calculated by Nearest Neighbourhood method or
by Bipolar Interpolation. Orthorectified imagery has
broad applications in both photogrammetric and GIS
fields.
3.3 Digital Elevation Models Generation
PhoTopoL DEM Generation version enable users to
generate DEMs automatically from image stereo pairs.
Special algorithm for image stereo pair correlation was
developed for PhoTopoL in Laboratory of Computer
Vision at Czech Technical University (see [7]). By us-
ing these stereo correlation algorithms, the system is
able to extract elevation values from image stereo pair.
The system uses pyramid method during correlation
process. The output are single points with informa-
tion about results of correlation stored in joined exter-
nal database. These values can serve for selection of
points used for created DEM. PhoTopoL is equipped
with own module for small- and middle-scale DEM
generation, which is able transform point collections
as well as contour lines into raster DEM form. After-
wards Raster DEM forms primary base for orthorec-
tification process in all versions of the PhoTopoL sys-
tem.
PhoTopoL provides also direct link to ATLAS system,
which is another Czech product developed for specific
tasks of DEM creation, edit, calculations, analyses and
visualization. ATLAS enables users to create flexible
elevation models for generating contour lines from se-
lected points. This module includes a powerful engine
for adding and editing breaklines and obligatory lines,
perspective three-dimensional views, profile calcula-
tions etc.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996
us
va
pt
in
Cr
